The present techniques relate generally to polyolefin catalysts and, more specifically, to preparing a precursor compound for an unsymmetric metallocene catalyst, for using the precursor compound to prepare catalysts, and for employing the precursor compounds to prepare catalysts for polyolefin polymerizations.
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present techniques. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
As chemical and petrochemical technologies have advanced, the products of these technologies have become increasingly prevalent in society. In particular, as techniques for bonding simple molecular building blocks into longer chains (or polymers) have advanced, the polymer products, typically in the form of various plastics, have been increasingly incorporated into various everyday items. For example, polyolefin polymers, such as polyethylene, polypropylene, and their copolymers, are used for retail and pharmaceutical packaging, food and beverage packaging (such as juice and milk bottles), household containers (such as pails and boxes), household items (such as appliances, furniture, carpeting, and toys), automobile components, pipes, conduits, and various industrial products.
Specific types of polyolefins, such as high-density polyethylene (HDPE), have particular applications in the manufacture of blow-molded and injection-molded goods, such as food and beverage containers, film, and plastic pipe. Other types of polyolefins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), isotactic polypropylene (iPP), and syndiotactic polypropylene (sPP) are also suited for similar applications. The mechanical requirements of the application, such as tensile strength and density, and/or the chemical requirements, such thermal stability, molecular weight, and chemical reactivity, typically determine what polyolefin or type of polyolefin is suitable.
To achieve these properties, various combinations of reaction systems may be used. For example, to form lower density products, such as LDPE and LLDPE, among others, two monomers may be polymerized together, i.e., co-polymerized. This forms a polymer that is described as having “short-chain branching.” Other polymers may have links between chains formed, called “long-chain branching,” while yet other polymers may have minimal branching of either type. Favorable properties may be obtained for polymers that are formed as in-situ blends of these types of branched polymer chains, such as in a single reactor using two different catalysts. The properties obtained for these blends may be determined by the molecular weights of each of the polymers and by which polymer is branched, e.g., short or long chains, among others. To obtain polymers having high strength and ease of processability, the branching should generally be confined to the higher molecular weight polymer. Accordingly, continuing efforts in catalyst research are directed towards developing mixed catalyst systems that may be used to form in-situ polymer blends, as well as more efficient ways of making these mixed catalyst systems.